Tunable magnetron



June 3, 1947.v E. D. MCARTHUR Erm.

TUNABLE MAGNETRON Filed May 29, 1944 Vlg. l

l1v1 van si Elmer D. MC Arthu Ral ph JBohdley,

Their Attorney.

Patented June 3, 1947 unir-Efo 4smutis 2,421,63m fruwusnli: MAeNEritoNf' 'Elmer tD; rMcAttlnm; Schenectady,- fandfalph Electric Company,y a

8 Claims. 1f- Our` invention Vrelates -to1ultra high frequency generators .and 'itt 'has :for :its'obJ'eCt' toA provide a corporation lof; Newi York a Application'MayjZE), 1944,-1Seria1 No'. 537,894 (Cll-e-.SSJS 1 newsand improved. ultra thigh: frequency generexciting :or -reson-atinga` portionofv a lconcentric l transmission linesv It is still anotherobject `of 'our invention-to provide afnewrand :improved magnetron f tube and circuit *arrangement iin which :the #frequency of the :electromagnetic WavesV generated therein-may be adiustedfover a substantial range.'

Briefly :statedzlour|` invention` :employs a -1reso= nantnz cavity 1 of fthe concentric transmission lline type'whichis excited/by asrotating electron eldproduced byfthe interaction of "an electron discharge and a funiform magnetic field". The inner conductor `o1 thefconcentric. transmission-line functions 'bothl as :an`- anodeV forthe discharge and 'fa :source f of: magnetic iield appliedY 'per-peri#L dicular :to saidf discharge. v` Means 1 .aref provi-ded for` adjusting fthe rfrequency .of- 'oscillations withl in the cavitysresonator-by .changing zthe .'lengthf of :the -concentric transmission s line s Without Pal-2 teringvthe continuity iof ithefmagnetic circuit fof: the magnetron.

The novel features :which webelieve .to lbe 1characteristic of 1 ourUA invention are i-set forthciwith; particularityin-V the 4appended claims. .Y Oiirixim., ventiony itself;y together "with its .further ufobieots; and'k advantages; may best fbe `understood-:Joy :refe erence to `thefollovving description taIcenfinvconjunction` with `theY accompanying drawing;` in. which 1ig. l is-avertical` section of a magnetrons tube-and circuit,lsuitably:embodying-the @inven-l tion .and Figi, 2V4 is enlarged .perspective avievv;y partly in section. and partly exploded, ofthe-mag., netron'tube ofFig. 1.:

Referring toFigs. 1 and 2 jointly, there is. shownw a .cavity resonator-.I yof the concentric..transmis-` sion line 4.ty,pe-.wl1ich ,comprises a., tubular-router conductor. 2 .and a centrally disposed. inner conf ductor., 3.. At one. end. ofl the Vcavity resonator; the .f inner conductorn 3 `is maintained inY coaxial. relation with respect to the outer` conductora!A by means of .a .metallic 4spacing ring .4 andcat its opposite end,. the resonator is `closeduoy an electron. .discharge device 5 -which serves :both to .supf port and. terminate Atheinner conductor 3.: I

The electron. discharge .device 5 is of `theijmaggcoaxiallyaligned vwith the inner conductor 3. Concer-itricallyA surrounding the cathode 6 f are 'a plurality if` yanode Vsegrnents 4'I 1(see 2); condu-ctively l connected 'to innerl conductor` 3 Inand forming anfextension thereofv and an equalnum berwof anode segments `18 supported by and'conductively` connected "-to-'a1-metallic `cup member 9 which isformed integrally :with a metallic disk IUS Tlieanodesegments uI 'randfare in interleaved fspaced `relation `andleach oflthe segments 'l Fis lcated- 'diametrically A`1across the center of cathode yUf-frein' a tcorresponding anode'. segment 8.2 Moreoventhe members are-spaced apart by #equal angular distancesu The-,.anodesegments 1 are connectedtomnfanodercap or-connector vI I Whichris in screws-threadedengagement With-the innerconductor- 3.? They-segments -1, B-f-are maintained: lin a fixed Avspaced :relation by means ofA 4a vitreous-member vor envelope I2 vwhich surrounds the vanode"-eath'ode"-A structure and is :hermetically hermeticallyaseale'd to sleeve- I 3 by 1 means lof ani insulatingstubetf For this purpose `the sleeve I3 :and-:capxll 5 :preferably .are formed Joranv iron'- nickel'fcobalt alloy. :andrthen seal I 6 yis -lformedrof.

aixboroesilicate glass. Afle'adflvwhich.- passes through: the tube :I 4 :and is .connected to the `other terminal of-.fthe vcathode :heating element` `is :in:- sulated fromathe-capz-,QIS 1 by. Lmeansfof a glass in` sulatin'g rbeadr I8 sealed across. `the s end 'offthe tube after 4the .l device .alias been evacuated.: In:

the tube :structurefthe anodeV segmental, y8 fpreff, erably' are Aformed-1f of: e, a goodr conductive non.- Vmagnetic:,material,; suchfas f copper, k While the anode connector lrII.the inner conductor-3, and the A.'metallicdisk :Im are: formednoffironfwhichfis,

plated; with Ya good-` conductivematerial-,1` such as copper; inferderwto provide.1.aslow. resistanceipath for high frequency currents; The` outer lconductory` '2f on 'the :other hand, l is formedfof- 1a 4nonmagnetiof: material; suche asf` copperf orY brass.:-

WhereIf-thesdevice gisfito operate -at fa: single V"free quency.l the tube -envelopefmay @enclose :gaga choke onelter notwshnwn fon-the cathode leadsto maintain the, cathode :at: proper potentialawith respect tothe anode.L

Aamagnetioeld: structure 4:provided for- :the netronetypetand.comprises.a.cathodemember 6 55- cavity `resenatcns-I Ifandftheelectricdishalgf is provided with a shoulder 22 against which theA magnetic disk Il) of device -5 abuts and is held in position by means of a threaded ring 23.

In the operation of the -ultrahigh frequency.

generator thus far described, a space charge is assumed to be developed in the space between'the cathode 6 and the surrounding anode structureby the application of a suitable potential im- 4 loop 28 is connected to the inner conductor of a concentric transmission line 29.

In constructing a magnetic iield structure for a magnetron, it has been observed that leakage iiux is kept at a minimumprovided the ratio of the inner diameter of the magnet I9 to the outer diameter of the rod 3 is greater than a value of 2. Accordingly, itis' contemplated in thek construction of the magnetron circuits described that the inner conductor 3 be a relatively small copper-plated iron rod. In the composite magnetron structure and circuit, therefore, due

Vto the concentric line structure of the cavity pressed between the cathode lead-in tube I4 and the conductor 3 serving 'as an anode lead-in conductor. The electrons which compose this space chargeare given a spiral or orbital motion-.by the uniformmagnetic field which exists between theends of the anode connector II and the cup member 9 serving as magnetic pole pieces to provide a magnetic iield which is parallel to the axis of the device 5. vUnder oscillating conditions, an alternating voltage exists between the outer conductor 2, to which is conductively connected the anode segments 8, and the inner conductor 3, to which is conductively connected the anode segments I and, therefore, alternate sections of the compositefanode structure are atany instant of opposite polarity. The anode segments 'I and 8 carry diiferent alternating potentials to the space charge region surrounding cathode 6 and superimpose the alternating potentialon the Vunidirectional electromagnetic eld already existing between the cathode and the surrounding anode structure.l Because of the interleaving of the anodesegments 1, 8, any two adjacentsegments vare of cppositelpolarity for alternating currents. The presence of this alternating current field in the space charge region causes the electrons vof the discharge to bunch together-in groups so that the operation of the device is similar to the operation of a conventional magnetron.

Means are also provided for adjusting the frequency of the oscillations developed within the cavity resonator I and which'comprise an adjustable annular plunger 24 provided with springlikeV iingers 25, 2E contacting, respectively, the inner surface of conductor 2 and the outer surface of conductor 3. The plunger 24 preferably is formed of a magnetic material, such as iron, and the iingers25, 26 and the surface of the plunger therebetween are provided with a good conductive coating, such as a copper plating. The plunger V2li may be moved axially to serve as an end wall forthe cavity resonator I, such movement being eifected by anyV suitable means, such as the `adjusting rod 21. The frequency of the oscillations developed within the cavity resonator Iisdetermined by the length of the section of transmissionline between the metal disk I9 and the plunger 24. Accordingly, the longest velectromagnetic wave which can be established within the magnetron tube has a length which is equal to about four times the electrical distance between these short-circuiting members. Y The axial length of the pole piece is adjusted to provide a desired range of wave length for the use contemplated. Energy may be abstracted from resonator l by any suitable output electrode means, such as the loop 28 carried by plunger 24. The

resonator, substantially no ultra high frequency electromagnetic eld exists outside the cavity resonator defined by the conductors 2, 3 and, at the same time, leakage magnetic flux is kept to a minimum value.

In the foregoing description, the magnetic structure I9 has been disclosed as of the permanent magnet type. It is apparent, however-,that other types of magnetic structures usingenergizing windings may be employed in conjunction with the particularly high frequency tube structure disclosed. Y

While we have shown a particular embodiment of our invention, it will of course beunderstood that we do not wish to be limited thereto since various modifications may be made, and we contemplate by the appended, claims to cover any such modications as fall within the true spirit and scope of our invention. i

What weV claim as new and desire to secure by Letters Patent of the United States is:

1. High frequency electrical apparatus com- Y prising an electric discharge device comprising a cathode, a pair of anode segments positioned on opposite sides ofsaid cathode, a transverse magnetic member connected to one of said segments, a longitudinal magnetic member connected to the other of said segments, dielectric means sealed between said members forming'an envelope f or said device, a tubular conductor conductively connected to said transverse member and concentrically surrounding said longitudinal member forming therewith a cavity resonator, and means for producing rotation of electrons emitted bysaid cathode comprising .magnetic means surrounding said outer conductor and magnetically coupled to said members. f l I 2. High frequency electrical apparatus coinprising an electric discharge device comprising a cathode, a pair of anode segments positionc'edl on opposite sides of said cathode, a. transverse mag;` netic member connected to one of said segments, a longitudinal magnetic member connected to the other of said segments, dielectric means sealed between said members for forming an envelope for said device, a tubular conductor conductively connected to said transverse member and concentrically surrounding said longitudinal member forming therewith a, cavity resonator, means for producing rotation of electronsl emitted'Y by said cathode comprising magnetic means surrounding said outer conductor and magnetically connected to said members,l and means for adjusting the Vresonance frequency of said resonator including an adjustable element positioned between said members.

' 3. High frequency electrical apparatus comprising an electric discharge device comprising a cathode, a transverse magnetic member, a longitudinally extending magnetic member, a plurality of rst anode segments conductively connected to said transverse member, a plurality of second anode segments in spaced interleaved relation with said first segments and conductively connected to said longitudinal member, dielectric means sealed between said members constituting an envelope for said device, a tubular conductor connected to said transverse member and concentrically surrounding said longitudinal member and forming therewith a cavity resonator, and a permanent magnet concentrically surrounding said tubular member and magnetically connected between said transverse member and said longitudinal member.

4. High frequency electrical apparatus comprising an electric discharge device comprising a cathode, a transverse magnetic member, a longitudinally extending magnetic member, a plurality of first anode segments conductively connected to said transverse member, a plurality of second anode segments in spaced interleaved relation with said first segments and conductively connected to said longitudinal member, dielectric means sealed between said members constituting an envelope for said device, a tubular conductor connected to said transverse member and concentrically surrounding said longitudinal member and forming therewith a cavity resonator, a permanent magnet concentrically surrounding said tubular member and magnetically connected between said transverse member and said longitudinal member, and a movable magnetic plunger positioned between said tubular conductor and said longitudinal member for adjusting the resonance frequency of said resonator.

5. High frequency electrical apparatus comprising an electric discharge device including an even number of elongated anode elements Dositioned in mutually spaced generally parallel relation and providing a generally circular array, a disk-like terminal member supporting alternate ones of said elements, a second terminal member supporting the remaining anode elements, an enclosure member of generally circular cross section having one end sealed to one face of said disk-like terminal member and the opposite end sealed to said second terminal member, a cathode supported within said array of anode elements, a cavity resonator including a generally cylindrical conductor connected with said second terminal member and a larger hollow cylindrical conductor electrically connected to said disklike terminal member.

6. An electric discharge device comprising a disk-like terminal member, a plurality of anode segments supported from said member and extending in a direction substantially perpendicular thereto, a second terminal member of smaller diameter than said disk-like terminal member, a plurality of anode segments equal in number to the segments supported by said disk-like terminal member supported from said second terminal member, a generally cylindrical enclosure means sealed at one end to said disk-like terminal member and at the opposite end to said second terminal member to support said terminal members with the anode segments supported thereby in interleaved relation with adjacent anode segments of the resulting array connected to different terminal members, and a cathode positioned within the array of anode elements and supported from one of said terminal members in insulated relation with respect thereto.

7. High frequency electrical apparatus comprising an electric discharge device including a cathode, a plurality of anode segments positioned in generally cylindrical array around said cathode, a magnetic member positioned at one end of said array supporting selected ones of said seg-ments, a longitudinal magnetic member positioned at the other end of said array supporting the others of said segments, means constituting a part of said device forming an hermetically sealed enclosure for said cathode and anode segments, a tubular conductor conductively connected to said first mentioned member and concentrically surrounding said longitudinal member forming therewith a cavity resonator, said members delining a magnetic path for magnetic fields directed parallel to the axis of said array and between said cathode and said anode segments.

8. High frequency electrical apparatus comprising an electric discharge device including a cathode, a plurality of anode segments positioned in generally cylindrical array around said cathode, a magnetic member positioned at one end of said array supporting selected ones of said segments, a longitudinal magnetic member positioned at the other end of said array supporting the others of said segments, means constituting a part of said device forming an her-metically sealed enclosure for said cathode and anode segments, and a tubular conductor conductively connected to said rst mentioned member and c oncentrically surrounding said longitudinal member forming therewith a cavity resonator, said members defining a magnetic path for magnetic iields directed parallel to the axis of said array and between said cathode and said anode segments, and means for producing rotation of electrons emitted by said cathode comprising magnetic means surrounding said outer conductor and magnetically coupled to said members.

ELMER D. MCARTHUR. RALPH J. BONDLEY.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Great Britain Jully 11, 1939 

